Mobile communications terminal smart card

ABSTRACT

A SIM for a mobile station used in a GSM mobile communications system the SIM operating system being adapted to perform data coding format conversion for data items stored in the SIM and transmitted to the mobile station. This ensures that the SIM is able to receive, and present, data items in the required standard format at the interface between the mobile station and the SIM, while allowing the data items to be stored in a compressed format in the SIM memory, thereby increasing the perceived storage capacity of the SIM.

BACKGROUND OF THE INVENTION

This invention relates to a smart card for a user station used in amobile communications system, such as a subscriber identity module (SIM)as used in a GSM (Global System for Mobile communications) digitalcellular radio system, to a mobile station including such a smart card,and to a method of transmitting data items to and from such a smartcard.

In a known conventional GSM system, each mobile station, such as amobile telephone handset, is provided with a SIM, herein also referredto as a smart card, which is inserted into the mobile station in orderto allow the mobile station to receive service in a GSM network.

A typical SIM includes a microprocessor, memory elements including apermanent memory (e.g. ROM), a non-volatile rewritable memory (e.g.EEPROM) and a volatile rewritable memory (e.g. RAM), and contacts forforming the data transfer interface between the SIM and the mobilestation.

The GSM standard also specifies a command set for use by a mobilestation to access data records in the SIM and retrieve and write datafrom and to the SIM. Such data records may be permanent data records,such as a record of the international mobile subscriber identity (IMSI)whereby the mobile subscriber is recognised by a mobile communicationsnetwork.

Other data records are modifiable, either at the initiative of themobile station (such as the data record holding the current locationarea information (LAI) for the mobile station) or at the initiative ofthe mobile subscriber (such as an abbreviated dialling number (ADN)record which is used to allow the subscriber to automatically initiatecalling of the stored dialling number by selection of the associateddialling number identifier when displayed by the mobile station).

Other modifiable data records include a short message data record, whichstores data relating to one or more short messages in alphanumericcharacters received by the mobile station, for future retrieval by thesubscriber.

For more details of the records which may be stored in a SIM, referenceshould be made to GSM Technical Specification 11.11 (ETS 300 608).

The memory capacity of the SIM is necessarily limited, primarily due tocost considerations.

Accordingly, the data records referred to above are limited in size andnumber in accordance with the memory capacity of the SIM, which can be adrawback. For example, in the case of ADN records, it is conventional toallocate sufficient memory capacity dedicated to an ADN list such thatup to 90 ADN records can be provided. Some subscribers however require agreater ADN storage capacity. This is evidenced by the fact that ADNstorage capacity is used as a positive marketing point by suppliers whoare able to provide SIM's having relatively large ADN storagecapacities. However, with a fixed amount of total memory capacityavailable, an increase in the memory capacity allocated to ADN recordsmust be compensated for by a reduction in the memory capacity allocatedto other data records.

Further information relating to known subscriber identity modules usedin GSM may be found in Farrugia A J et Al.: “Smard Card TechnologyApplied to the Future European Cellular Telephone on the digitalD-Network”, selected papers from the Second International Smart Card2000 Conference, Oct. 4-6 1989, Amsterdam, NL, 1991, pages 93-107.

GB-A-2251357 describes a radio telephone terminal which includes aterminal unit having a transmitter-receiver and an external device. Theexternal device has a storage unit for storing subscriber information, arecaller unit for selectively recalling the stored information.Information may be recalled from the external device to the radiotelephone unit, so that it is possible to originate a call from theterminal unit using a subscriber telephone number stored in the externaldevice without the need for a dialling operation on the terminal unit.Thus, subscriber information stored in the terminal unit may beaugmented by subscriber information stored in the external device.

U.S. Pat. No. 4,875,230 describes a cellular telephone which includeslogic circuitry allowing keystroke sequences to be stored and recalledfor activation using a short form recall command. It does not describethe use or a smart card.

BRIEF SUMMARY OF THE INVENTION

The present invention in one aspect provides a smart card for a mobilestation used in a mobile communications system, said smart cardincluding:

a memory for storing data items communicated via an interface betweensaid card and said mobile station; and

data item converting means,

said converting means being for receiving a data item transmitted viasaid interface in a standardised data coding format, for converting saiddata items to a compressed data coding format and for storing said dataitem in said memory in said compressed data coding format, and

said converting means being for receiving said data item from saidmemory in said compressed data coding format, for decompressing saiddata item to said standardised data coding format and for transmittingsaid data item via said interface in said standardised data codingformat.

Thus, even if a standardised data coding format for a data itemtransmitted via the smart card/mobile station interface is not optimalfor storage, by use of the present invention the data item can still bestored in the smart card in a compressed data coding format, withoutrendering the smart card incompatible with the chosen standard.

The data coding format conversion can be implemented invisibly to themobile station. That is to say, the communication of data items via theinterface between the smart card and the mobile station can beimplemented in the data coding format required by the chosen standard,irrespective of the data coding format used for stored items.

Thus, the smart card can remain compatible with all mobile stationscomplying with the chosen standard.

In some cases, data items are required to conform to a standardisedfixed length data coding format when communicated to or from the mobilestation. The data item converting means then preferably converts dataitems from said fixed length data coding format to a variable lengthdata coding format. More efficient data coding can thereby be achieved.For example, in the case of ADN records, the use of a variable lengthcoding format for storage of ADN data items can increase the amount ofADN records available, compared to the conventional storage format, byover 50%. Thus, the number of ADN records available can be increased toover 100, without increasing the memory allocated to the ADN list.

The data items may comprise a variable Quantity of non-padding characterdata (i.e. data relating to useful information), and when in thestandardised data coding format a variable quantity of padding data(i.e. data of which the contents are ignored). The data item convertingmeans is preferably operable to reduce the amount of padding data whenconverting the data items to the different data coding format. Dataitems can then be stored in a more compact coding format in a givenallocation of memory capacity.

In a further aspect, the invention provides a method of writing a dataitem to, and transmitting a data item from, a smart card for a mobilestation used in a mobile communications system, said card including amemory for storing data items communicated via an interface between saidcard and said mobile station, wherein said method comprises:

receiving a data item transmitted via said interface in a standardiseddata coding format, converting said data items to a compressed datacoding format and storing said data item in said memory in saidcompressed data coding format; and

receiving said data item from said memory in said compressed data codingformat, decompressing said data item to said standardised data codingformat and transmitting said data item via said interface in saidstandardised data coding format.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way ofexample only, with reference to the accompanying drawings in which:

FIG. 1 is a block diagram of a mobile communications network;

FIG. 2 is a block diagram of a mobile station;

FIG. 3 illustrates the structure of a linear fixed data file;

FIG. 4 illustrates the structure of a fixed length data record;

FIG. 5 illustrates a standard coding of typical dialling numbers;

FIG. 6 illustrates a principle of the present invention;

FIG. 7 illustrates the structure of a data file according to the presentinvention;

FIG. 8 illustrates the structure of data record according to the presentinvention;

FIG. 9 illustrates the coding of typical dialling numbers according tothe present invention;

FIG. 10 is a flow diagram showing a procedure followed by the SIM of amobile station when reading an ADN record in accordance with the presentinvention; and

FIG. 11 is a flow diagram showing a procedure followed by the SIM of amobile station when updating an ADN record in accordance with thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

A GSM network, referred to as a public land mobile network (PLMN), isschematically illustrated in FIG. 1. This is in itself known and willnot be described in detail. A mobile switching centre (MSC) 2 isconnected via communication links to a number of base station controller(BSCs) 4. The BSCs 4 are dispersed geographically across areas served bythe mobile switching centre 2. Each BSC 4 controls one or more basetransceiver stations (BTSs) 6 located remote from, and connected byfurther communication links to, the BSC. Each BTS 6 transmits radiosignals to, and receives radio signals from, mobile stations 8 which arein an area served by that BTS. That area is referred to as a “cell”. AGSM network is provided with a large number of such cells, which areideally contiguous to provide continuous coverage over the whole networkterritory.

A mobile switching centre 2 is also connected via communications linksto other mobile switching centres in the remainder of the mobilecommunications network 10, and to other networks such as a publicservice telephone network (PSTN), which is not illustrated. The mobileswitching centre 2 is provided with a home location register (HLR) 12which is a database storing subscriber authentication data including theinternational mobile subscriber identity (IMSI) which is unique to eachmobile station 8. The IMSI is also stored in the mobile station in asubscriber identity module (SIM) along with other subscriber-specificinformation.

The mobile switching centre is also provided with a visitor locationregister (VLR) 14 which is a database temporarily storing subscriberauthentication data for mobile stations active in its area.

Referring to FIG. 2, a mobile station 8 comprises a transmit/receiveaerial 16, a radio frequency transceiver 18, a speech coder/decoder 20connected to a loudspeaker 22 and a microphone 24, a processor circuit26 and its associated memory 28, an LCD display 30 and a manual inputport (keypad) 32. The mobile station is connected to a removable SIM 34via electrical contacts 35.

The SIM 34 connected to the mobile station has a SIM processor 36, forexample a Hitachi H8 microprocessor, and SIM memory 38, which includesfor example 16 kilobytes of mask-programmed ROM 38 a containing the SIMoperating system, 8 kilobytes of read/write EEPROM 38 b for thenon-volative storage of data items and 256 bytes of RAM for use by theSIM processor 36 during operations.

At present, two physical formats of SIM are specified by the GSM and ISOstandards. The first is referred to as an ID-1 SIM, which is a removablesmart card complying with the ISO 7816 standard and being of similardimensions to that of a conventional credit card. The second is referredto as a plug-in SIN, which is a smart card of the same thickness as theID-1 SIM, but only measuring 25 millimetres in length and 15 millimetresin width.

Both the mobile station 8 and the different formats of SIM 34 are wellknown and therefore need not be described in detail herein. Acommercially-available SIM is the GemXplore (registered trade mark) SIMcard produced by Gemplus, BP 100-13881, Gemenos Cedex-France.

As described above, the SIM 34 is used for the storage and retrieval ofdata items by the processor 26 of the mobile station 8. The command set,data file structure and data coding format for data communicated via theinterface between the mobile station processor 26 and the SIM processor36 are all specified, in the GSM system, in GSM technical specification11.11.

A standard GSM file structure for the storage of data on a SIM, referredto as a linear fixed file structure, is illustrated in FIG. 3. Itconsists of a header 40 and record space 42. The record space is dividedinto N fixed length records.

One example of data record provided in the SIM memory 38 in aconventional SIM 34 is an abbreviated dialling number (ADN) record 44,which forms part of an ADN list file having a linear fixed filestructure. Each ADN record 44 has data stored in a fixed length codingformat. The record 44 is divided into fixed-length data blocks, eachconsisting of one or more bytes. A first data block 46, consisting of nbytes, is reserved for data relating to a dialling number identifier,such as a person's name, or a company name. A second block 48,consisting of one byte, is reserved for data indicating the length ofthe dialling number. A third block 50, consisting of one byte, isreserved for data indicating the type of dialling number stored in therecord. A fourth block 52, consisting of 8 bytes of memory, is reservedfor the dialling number data itself, coded in extended BCD coding asdefined in GSM Technical Specification 11.11. A fifth block 54,consisting of one byte, is reserved for a “capability configurationpointer”, indicating the bearer services (e.g. voice call, fax, etc.)which can be supported by the telephone equipment corresponding to thedialling number stored. A final data block 56, consisting of one byte,is an extension record pointer, which indicates the address of anextension record to be accessed in a different data file to give theremainder of a dialling number. The extension record pointer is usedonly in the rare case that the dialling number is longer than can bestored in the allocated data block 52.

Referring to FIG. 5, data items relating to three typical diallingnumbers and their associated dialling number identifier are shown codedin the standardised format. Each nibble (four bits of data) is indicatedin hexadecimal notation. It will be seen that the coded data consistsnot only of useful character data, but also of padding data (in thiscase hexadecimal “F”s) which is added to fill unused memory space in thefixed-length record. Thus, for the dialling number identifier “home”, 4bytes are used for coding the character data, whereas in this case 10bytes are available. The remaining 8 bytes are filled with padding data.The length of number indicator (“07”) is coded in one byte, and the typeof number code (“81”) is coded in the next byte. The dialling numberitself is stored in a nibble-swapped coding format, that is to say that,in each byte, the nibbles are coded in reverse order. The character datacorresponding to the dialling number “01234 567890”, occupies 5½ bytes,and 4½ bytes of the data block 52 are filled with padding data. As isgenerally the case, no extension record data or capability configurationpointer data is available. The last two data blocks 54 and 56 aretherefore also filled with padding data.

The principle of this embodiment of the present invention is illustratedin FIG. 6. In accordance with this embodiment of the invention, astandardised data coding format need only be used selectively incommunications between the mobile station 8 and the SIM 34. Data istransmitted between the SIM processor 36 and the SIM memory 38 in adifferent data coding format to that used across the communicationsinterface 58 between the SIM processor 36 and the mobile stationprocessor 26.

In the case of the present embodiment, the operating system stored inthe ROM of the SIM processor 36 is adapted to compress and decompressdata communicated between the SIM memory 38 and the interface 58. Thatis to say, the data coding format used in records provided in the SIMmemory 38 is not the same as that used when those data records arecommunicated across the interface 58 to and from the mobile stationprocessor 26.

This allows a more compact data coding format to be implemented in theSIM memory 38, whilst the SIM itself conforms with a prescribed GSMstandard.

Referring now to FIG. 7, a new file structure is provided forvariable-length data records in the SIM. This file structure includes aheader portion 60, a directory list 62 and record space 64. The header60 consists of 2 bytes of data, the first indicating the average lengthof records in the record space 64 and the second indicating the numberof valid records in that space. The directory list 62 is divided into Nblocks which provide storage space for addresses, or offset addressvalues, for up to N data records in record space 64. The record space 64contains the variable length ADN data records.

A data coding format for an ADN data item when stored in record space 64is shown in FIG. 8. The ADN record 66 consists of various data blocks. Afirst fixed length data block 68, consisting of one byte, has individualbits allocated for various information. One bit is reserved for anextension record flag, a second is reserved for a capabilityconfiguration flag, a third bit is available for storage of otherinformation, and five bits are allocated for indicating the byte lengthof the record. A second, variable length, data block 70 consists of nbytes, containing the dialling number identifier data. Each of thesebytes is filled with non-padding character data, for example the name ofthe party to be called, coded in the 7-bit coded alphabet as defined inGSM Technical Specification 03.38, with the eighth bit of each byte setto zero. The length of the data block 70 corresponds with the length ofthe dialling number identifier.

A third data block 72 consists of one nibble with each of its bits setto “one”, i.e. hexadecimal “F”, to indicate the end of the diallingnumber identifier. A fourth, fixed length, data block 74, consisting ofone byte, is reserved for storing data relating to the type of diallingnumber stored in the record. A fifth, variable length, data block 76 isreserved for storage of message data, coded in the GSM extended BCDcoding number set representing the dialling number. The length of thedata block 76 corresponds with the amount of digits in the diallingnumber. A final data block 78, consisting of one nibble having each bitset to “one”, is an end marker indicating the end of the record.

FIG. 9 illustrates the same ADN data as was illustrated in FIG. 5, codedaccording to the compressed data coding format. The first byte of eachADN data item, indicated as “XY”, “WZ” and “UW” in each respective case,represents the new data created in data block 68. The remainder of eachdata item is the restructured character data relating to the diallingnumber identifier, the type of number identifier, and the diallingnumber itself. As can be seen, unnecessary padding data is eliminated inthe compressed data coding format. The only hexadecimal “F”s present arethose used either for coding the alphabetical characters or are thoseused as end of data block markers. It will be apparent from FIG. 9, whencompared with FIG. 5, that the data items when in the compressed datacoding format occupy significantly less memory space than when in thestandardised coding format.

The SIM operating system, implemented by the SIM processor 36, performsconversion between the compressed data coding format and thestandardised data coding format when writing data to the SIM memory 38and when retrieving data from the SIM memory 38. This ensures that thedata items communicated via the interface 58 to or from the mobilestation 8 are presented in the standardised data coding format, asrequired by the GSM standard.

If all data items occupied the allocated space in the fixed-lengthcoding format, no discernable data compaction would be obtained byimplementing the data coding format conversion method of the presentinvention. However, in practice since the standardised format is definedso that the SIM is capable of accommodating relatively long diallingnumbers, the majority of dialling numbers, and often also the diallingnumber identifiers, are shorter than the maximum length provided for. Asignificant amount of data compaction can therefore be achieved.

Referring now to FIG. 10, in order to access an ADN data record, themobile station processor 26 generates a “SELECT FILE” command selectingthe ADN list file, which is received by the SIM processor 36 at step 80.Next, the processor 26 generates a “READ RECORD” command, received bythe SIM processor 36 at step 82, specifying that record number n in thedata file is to be read. These commands are specified in GSM technicalspecification 11.11. A conventional SIM card would respond by readingrecord n in the linear fixed file and transparently transmitting therecord contents to the processor 26.

According to this embodiment of the present invention, the SIMprocessor, controlled by its operating system, first accesses thedirectory list 62 to identify the address of record n in the recordspace 64, step 84, and then reads the data beginning from that addressin the record space 64, step 86, the length of the record beingindicated by the length data stored in the first block 68 of the record.

The SIM processor 36 then decompresses the record contents by convertingfrom the compressed data coding format to the standardised data codingformat, adding the padding data where required to produce a data item ofa fixed length, step 88. This is then transmitted across the interface58 to the mobile station processor 26, step 90. The mobile stationprocessor 26 then copies this data item to its associated memory 28,where it is stored temporarily for retrieval whilst the mobile stationremains switched on.

Reference is now made to FIG. 11. When the mobile station processor 26wishes to write an ADN data item to the SIM 34, it generates a “SELECTFILE” command selecting the ADN list file, received by the SIM processor36 at step 92. Next, the processor 26 sends the data item in thestandardised data coding format across interface 58 to the SIM processor36 with an “UPDATE RECORD n” command, received by the SIM processor 36at step 94. The SIM processor then compresses the data by converting thedata into the compressed data coding format, step 96, and stores thecompressed data item in a newly created record at the end of the currentrecords in the record space 64, step 98. The SIM operating system thenmakes a corresponding entry in the directory list 62, step 100.

When data records are consecutively entered in the record space 64, therecords are contiguous. However, when a data record is deleted, orupdated, the memory space previously occupied by that data record isfiled with padding data (hexadecimal “F”s). In the case of a recordbeing updated with new data, a new record is created and stored at theend of the current records, since it cannot be guaranteed that therecord will be the same length once updated. Thus, when records aredeleted or updated, the record space 64 will become fragmented. In orderto overcome this, the card operating system periodically de-fragmentsthe records in the record space 64, by reading a data record adjacent anempty space (filled with padding data) in the record space 64 into abuffer memory space and rewriting the record at least partially into theempty record space, contiguous with the adjacent record.

If de-fragmentation were implemented immediately after updating ordeletion of a record, there would be a danger that the SIM could beswitched off, in response to a command from the mobile station 8, duringde-fragmentation, in which case it is possible that the data recordcontents could be lost. In this embodiment of the invention, the SIMoperating system performs de-fragmentation in steps in response to acommand (which is intended to perform a different function) periodicallysent to the SIM by the mobile station 8, such as a reset command.

A reset command is sent when the mobile station 8 is first switched on,and various initialisation steps are performed by the SIM processor 36on receipt of a reset command. Since the ADN list update frequency isassumed to be relatively low, it is not necessary to de-fragment theentire ADN list at each reset.

Instead, de-fragmentation is performed gradually and a limited number ofrecords, for example, 2 or 3, are de-fragmented per reset command. Thatis to say, 2 or 3 records are displaced in the record space 64 to occupythe space of a previously deleted or displaced record each time the SIMis reset. By this method, any delays experienced by the mobile stationuser, caused by de-fragmentation of the ADN list before the SIM isinitialised, can be reduced.

The SIM includes a counter data record, incremented at each resetcommand, which indicates the present record number up to whichde-fragmentation has been completed. The SIM processor 36 reads thevolume of this counter data record at each reset command to determinewhich records are next to be de-fragmented. Thus, for a heavilyfragmented record space 64, a large block of available memory space iscreated as the records are gradually compacted together byde-fragmentation. Once de-fragmentation is completed, for all currentrecords the SIM operating system resets the counter value and furtherde-fragmentation of the ADN list, if required, begins afresh at thefirst record in the record space when the SIM is again reset.

Other Embodiments

The data described has thus far been ADN data. However, it will beappreciated that the present invention can be applied to any other typesof data required to be transmitted across the mobile station/removabledata store interface according to the relevant standard in non-optimumdata coding formats.

In the GSM standard, other data is transmitted between the mobilestation and the SIM in a fixed length coding format similar to that ofthe ADN data, for which the present invention is therefore similarlyapplicable. Such other data includes fixed dialling number (FDN) data,mobile subscriber directory number (MSISDN) data, extension record data,etc.

Furthermore, although in the above embodiment acompression/decompression method implemented by stripping padding datafrom, and replacing padding data in, data items is used, alternative, oradditional, data coding format conversion methods are envisaged. Apartfrom the wasted memory space associated with padding data, many diallingnumbers contain frequently repeated dialling codes. For example, thedialling code for mobile stations subscribing to a particular mobilecommunications network may have a dialling code of “0973”. Replacingthis code with a token code of shorter length could be implemented bythe SIM operating system before storage of the dialling number in theSIM memory, with replacement of the code in its full length beingimplemented when the dialling number is retrieved from the SIM memory bythe SIM operating system.

It is to be noted that the data format conversion need not necessarilybe performed in the SIM. For example, a mobile station can beimplemented which transmits (or receives) data items across theSIM/mobile station interface both in a standardised data coding format(such that the mobile station remains compatible with conventional SIMs,and therefore conforms to a standard), and in a compressed data codingformat, such that a SIM in accordance with the present invention canstore the data items received in the compressed data coding format, anddisregard the standardised data coding format items.

Although the above description has related to a SIM used in aGSM-compatible mobile station, it should be appreciated that the presentinvention is applicable to equivalent forms smart card used in any othermobile communication system. References to GSM include other standardsfor which at least some features, in particular with regard to themobile station/SIM interface, are set by the GSM technicalspecifications, such as the PCN standard and the DCS 1800 standard.

Other variations, improvements and modifications are also envisaged tofall within the scope of the present invention.

What is claimed is:
 1. A smart card for a mobile station, having a firstdata processor, utilized in a mobile communications system, the smartcard comprising: an interface capable of transferring data items fromand to the mobile station; a memory capable of storing the data items;and a second data processor interacting with the first data processor byreceiving data items therefrom, and transmitting data items thereto, ina predetermined coding format, such that the smart card is compatiblewith different mobile stations implementing a common mobilestation/smart card interfacing standard, and storing and retrieving thedata items to and from the memory, wherein the second processor isadapted to convert a data item received via the interface from thepredetermined coding format to a compressed coding format and to storethe data item in the memory in the compressed coding format, and whereinthe second processor is adapted to convert the data item, when retrievedfrom the memory, from the compressed coding format to the predeterminedcoding format before transmitting the data item via the interface in thepredetermined coding format, wherein the compression and decompressionis performed on the smart card to reduce the amount of memory occupiedby the data item on the smart card, without diverging from the mobilestation/smart card interfacing standard.
 2. The smart card according toclaim 1, wherein the predetermined coding format comprises a fixedlength coding format and the compressed coding format comprises avariable length coding format.
 3. The smart card according to claim 2,wherein the data items comprise a variable amount of non-paddingcharacter data when in the fixed length coding format.
 4. The smart cardaccording to claim 3, wherein the data items have lengths varying inincrements of one character when in the variable length coding format.5. The smart card according to claim 1, wherein the data item comprisesdata representing alphanumeric characters.
 6. The smart card accordingto claim 5, wherein the data item comprises data representing a dialingnumber and/or a dialing number identifier.
 7. The smart card accordingto claim 1, wherein the data item comprises information input by a userfor subsequent retrieval.
 8. The smart card according to claim 1,wherein the data item comprises padding data when in the predeterminedcoding format, and wherein the second processor reduces the amount ofpadding data when converting to the compressed data coding format. 9.The smart card according to claim 1, wherein the data item is stored inone of a plurality of data records in an allocated data file in thememory, the data file having an associated directory file storing anaddress for each data record, wherein the second processor is adapted todelete a data record from the data file and to (i) displace another datarecord to occupy memory space previously occupied by the deleted record,and (ii) update the directory file, and wherein the second processor isadapted to perform (i) and (ii) in response to a command sent by themobile station subsequent to the deletion.
 10. The smart card accordingto claim 9, wherein the command comprises a reset command.
 11. The smartcard according to claim 1, wherein the smart card comprises a GlobalSystem for Mobile communications (GSM)-type subscriber identity module.12. The smart card according to claim 1, wherein the smart cardcommunicates data with a mobile station in a mobile communicationssystem.
 13. The smart card according to claim 1, wherein the standardcomprises a Global System for Mobile communications (GSM) standard. 14.A method of storing and retrieving a data item using a smart cardcommunicating with a mobile station of a mobile communications systemvia an interface, the smart card and the mobile station each conformingwith an identical mobile station/smart card interfacing standarddefining a predetermined format of data coding for a data item whentransmitted across the interface, the method comprising: (a) processingthe data item in the mobile station to ensure the data item is in thepredetermined format; (b) transmitting the data item in thepredetermined format to the smart card via the interface; (c) processingthe data item in the smart card, to compress the data item to acompressed coding format; (d) storing the data item in a memory in thesmart card using the compressed coding format; (e) retrieving the dataitem from the memory; (f) processing the data item in the smart card todecompress the data item from the compressed coding format to thepredetermined coding format, the compression and decompression beingperformed on the smart card to reduce the amount of memory occupied bythe data item on the smart card, without diverging from the mobilestation/smart card interfacing standard; and (g) transmitting the dataitem in the predetermined format from the smart card to the mobilestation.
 15. The method according to claim 14, wherein the predeterminedcoding format comprises a fixed length coding format and the compressedcoding format comprises a variable length coding format.
 16. The methodaccording to claim 14, wherein the data item comprises a dialing numberand/or a dialing number identifier.
 17. A smart card for a mobilestation, having a first data processor, used in a mobile communicationssystem, the smart card comprising: an interface capable of transferringdata items from and to the mobile station; a memory capable of storingthe data items; and a second data processor capable of interacting withthe first data processor by receiving the data items therefrom, andtransmitting data items thereto, such that the card is compatible withdifferent mobile stations implementing a common mobile station/smartcard interfacing standard, and storing and retrieving the data items toand from the memory, wherein the data items are stored in a plurality ofdata records in an allocated data file in the memory, the data filehaving an associated directory file storing an address for each datarecord, the second processor being adapted to delete a data record fromthe data file and to (i) displace another data record to occupy space inthe memory previously occupied by the deleted record, and (ii) updatethe directory file, and wherein the second processor is adapted toperform (i) and (ii) in response to a command sent by the mobile stationsubsequent to the deletion.
 18. The smart card according to claim 17,wherein the command comprises a reset command.
 19. A method of storingand retrieving a data item using a smart card communicating with amobile station of a mobile communications system via an interface, thesmart card and the mobile station each conforming with a predeterminedmobile station/smart card interfacing standard defining a predeterminedformat of data coding for a data item when transmitted across theinterface, the method comprising: (a) processing the data item in themobile station to ensure the data item is in the predetermined format;(b) transmitting the data item in the predetermined format to the smartcard via the interface; (c) processing the data item in the smart cardto compress the data item to a compressed coding format; and (d) storingthe data item in a memory in the smart card in the compressed codingformat.
 20. The method according to claim 19, additionally comprising:retrieving the data item from the memory, wherein retrieving the dataitem comprises processing the data item in the smart card to decompressthe data item from the compressed coding format to the predeterminedcoding format, and wherein the compression and decompression performedin the smart card reduces the amount of memory occupied by the data itemon the smart card, without diverging from the mobile station/smart cardinterfacing standard; and transmitting the data item in thepredetermined format from the smart card to the mobile station.